A responder is a person who responds to an event, situation or request. It can refer to someone who provides assistance in emergency situations such as medical professionals who rush to the scene of an accident to provide aid, or it could be anyone who reacts and takes action when needed. In general usage, the term responder is used to describe a person who responds to something, whether it's a request for information, a call to action, or any other stimulus that elicits a response from an individual.